Field of the Invention
This invention relates to a method of, and apparatus for, friction welding. The invention has been developed in relation to the welding of universal joint components to the ends of a shaft, the resulting assembly being intended for use in a motor vehicle.
If such an assembly is to be manufactured by friction welding the universal joint components to the ends of the shaft, apparatus may be used which comprises a holder for holding the shaft stationary and two chucks for holding the joint components at the ends thereof. The joint components are rotated rapidly in contact with the shaft until the material has reached an appropriate welding temperature, and the chucks are braked and a greater axial pressure applied to form the finished welds. Because of the inertia of the chucks holding the joint components, and their associated drive motors and brakes, they cannot be braked to a standstill instantaneously and the practical result of this is that during the application of welding pressure a succession of welds are, in effect, made and then torn apart. Only when all relative rotation has ceased does a final weld result. The result of this is a danger of unsatisfactory welds. The problem is particularly severe in the case of shaft assemblies made of aluminium alloys where the high thermal conductivity of the material gives rise to rapid cooling of the weld regions. The time in which a satisfactory weld can be established is reduced to a minimum.
It has been proposed, in British Patent No. 1,376,071, that when two components are being friction welded together, it can be helpful to enable both components to rotate during the welding phase of the process so that their speeds can synchronize more rapidly than if one component were held stationary throughout. However, the apparatus proposed is relatively complex.
It is the object of the present invention to overcome or reduce these disadvantages.